In the art, various processes for producing silicon for use as a raw material for semiconductors and photocells are known. Some thereof are already put into industrial practice.
For example, one prior art process is known as the Siemens process. In the Siemens process, a silicon rod having been heated to a silicon deposition temperature by current passages is disposed in a bell jar, and trichlorosilane (SiHCl3, hereinafter referred to as TCS) or monosilane (SiH4) together with a reducing gas, such as hydrogen, is brought into contact with the heated silicon rod to thereby cause the deposition of silicon.
This process is characterized in that a high-purity silicon can be obtained, and carried out as the most common process. However, deposition is performed batchwise, so that there is such a problem that an extremely complex procedure including arranging of a silicon rod as seed, heating of the silicon rod by current passage, deposition, cooling, takeout, bell jar cleaning, etc. is inevitable.
With a view toward resolving this problem, Japanese Patent Laid-open Publication No. 2002-29726 proposes a silicon production reactor capable of producing silicon stably and continuously over a prolonged period of time. In this silicon production reactor, while feeding a raw gas for silicon deposition into a tubular vessel capable of being heated to a temperature of not lower than the melting point of silicon, the tubular vessel is heated so as to perform deposition of silicon. The deposited silicon is continuously melted and caused to fall from the lower end of the tubular vessel, thereby attaining collection of silicon.
This reactor is a very excellent apparatus capable of resolving various problems of the conventional Siemens process and capable of continuous production of silicon. However, when a scale-up of the reaction vessel of cylindrical configuration, etc. described in Examples of Japanese Patent Laid-open Publication No. 2002-29726 is preformed as it is with an intent to produce silicon on an industrial scale of hundreds of tons or more per year, the reactivity of raw gas would inevitably drop. Further, fine powder of silicon and by-products such as low-molecular-weight polymers of silane compounds are likely to be generated, thereby tending to invite a decrease of silicon yield. In these respects, an improvement has been demanded.